The ultimatum from Berlin comes as Ukraine said Russia was still carrying out attacks along the front line, despite a ceasefire proposal agreed on the weekend among Kyiv's allies for a 30-day ceasefire to start Monday. The Kremlin said such an ultimatum "is unacceptable for Russia."

The chief of staff to Germany's new chancellor, Thorsten Frei, has called on Europe to step "out of our comfort zone" and impose tougher sanctions on Russia, such as banning gas and uranium imports and tapping into frozen Russian state assets.

European leaders agreed to increase pressure on Russia through sanctions after U.S. President Donald Trump briefed them on his call with Russian President Vladimir Putin, German Chancellor Friedrich Merz said late on Monday.